lattice xscale.components: different ticks on top/bottom axis

Fri, Apr 1, 2011 12:59 PM

On Fri, Mar 11, 2011 at 12:28 AM,  
<Boris.Vasiliev at forces.gc.ca> wrote:

Good afternoon,

I am trying to create a plot where the bottom and top axes have the 
same scale but different tick marks. ?I tried user-defined 
xscale.component function but it does not produce desired results. ?
Can anybody suggest where my use of xscale.component 
function is incorrect?

For example, the code below tries to create a plot where horizontal 
axes limits are c(0,10), top axis has ticks at odd integers, and 
bottom axis has ticks at even integers.

library(lattice)

df <- data.frame(x=1:10,y=1:10)

xscale.components.A <- function(...,user.value=NULL) {
?# get default axes definition list; print user.value
?ans <- xscale.components.default(...)
?print(user.value)

?# start with the same definition of bottom and top axes
?ans$top <- ans$bottom

?# - bottom labels
?ans$bottom$labels$at <- seq(0,10,by=2)
?ans$bottom$labels$labels <- paste("B",seq(0,10,by=2),sep="-")

?# - top labels
?ans$top$labels$at <- seq(1,9,by=2)
?ans$top$labels$labels <- paste("T",seq(1,9,by=2),sep="-")

?# return axes definition list
?return(ans)
}

oltc <- xyplot(y~x,data=df,

scales=list(x=list(limits=c(0,10),at=0:10,alternating=3)),
? ? ? ? ? ? ? xscale.components=xscale.components.A,
? ? ? ? ? ? ? user.value=1)
print(oltc)

The code generates a figure with incorrectly placed bottom and top 
labels. ?Bottom labels "B-0", "B-2", ... are at 0, 1, ... and top 
labels "T-1", "T-3", ... are at 0, 1, ... ?When axis-function runs out 
of labels, it replaces labels with NA.

It appears that lattice uses top$ticks$at to place labels and 
top$labels$labels for labels. ?Is there a way to override this 
behaviour (other than to expand the "labels$labels" vector to be as 
long as "ticks$at" vector and set necessary elements to "")?

Well, <top|bottom>$ticks$at is used to place the ticks, and 
$labels$at is used to place the labels. They should typically 
be the same, but you have changed one and not the other. 
Everything seems to work if you set $ticks$at to the same 
values as $labels$at:


    ##  - bottom labels
+   ans$bottom$ticks$at <- seq(0,10,by=2)
    ans$bottom$labels$at <- seq(0,10,by=2)
    ans$bottom$labels$labels <- paste("B",seq(0,10,by=2),sep="-")

    ##  - top labels
+   ans$top$ticks$at <- seq(1,9,by=2)
    ans$top$labels$at <- seq(1,9,by=2)
    ans$top$labels$labels <- paste("T",seq(1,9,by=2),sep="-")

Also, can user-parameter be passed into xscale.components() 
function? (For example, locations and labels of ticks on the top 
axis). ?In the  code above, print(user.value) returns NULL even 
though in the xyplot() call user.value is 1.

No. Unrecognized arguments are passed to the panel function 
only, not to any other function. However, you can always 
define an inline
function:

oltc <- xyplot(y~x,data=df,
               scales=list(x=list(limits=c(0,10), at = 0:10, 
                           alternating=3)),
               xscale.components = function(...) 
                           xscale.components.A(..., user.value=1))

Hope that helps (and sorry for the late reply).

-Deepayan

Deepyan,

Thank you very much for your reply.  It makes things a bit clearer.  

It other words in the list prepared by xscale.components(), vectors <top|bottom>$ticks$at and <top|bottom>$labels$at must be the same.  If only every second tick is to be labelled then every second label should be set explicitly to empty strings:

  ans$bottom$ticks$at <- seq(0,10,by=1)
  ans$bottom$labels$at <- seq(0,10,by=1)
  ans$bottom$labels$labels <- paste("B",seq(0,10,by=1),sep="-")
  # replace  "B-1", "B-3", ... with ""
  ans$bottom$labels$labels[seq(2,11,by=2)] <- ""

Sincerely,
Boris.

lattice xscale.components: different ticks on top/bottom axis

Thread (2 messages)